This invention relates generally to a cartridge for holding a hologram-image recording medium. The cartridge is mounted on a hologram-image recording apparatus for producing holographic stereogram. The holographic stereogram is capable of producing a three-dimensional rendition of either a photograph or an image produced by a computer.
A holographic stereogram is produced by imaging two pictures of a single object obtained by sequentially photographing the object from different observing points. These two pictures are sequentially exposed and recorded on one hologram recording medium as a collection of oblong or dot shaped elements. A user can identify a two-dimensional image, including an aggregate of image information of a portion of the hologram, when the user looks at the holographic stereogram through one eye from a certain position. When the user looks at the holographic stereogram from another position, the user can see a two-dimensional image, including an aggregate of image information of another portion of the hologram. Therefore, when the user looks at the holographic stereogram with both eyes, the parallax between the two eyes causes the recorded hologram to be observed as a three-dimensional image.
Such a holographic stereogram can be produced by a holographic stereogram producing apparatus 100 shown in FIG. 17 (A). Holographic stereogram producing apparatus 100 includes a laser-beam source 101 for emitting a single wavelength laser beam L10 exhibiting excellent coherency, and a partial reflecting mirror 102 for splitting laser beam L10 into an object laser beam L11 and a reference laser beam L12. Optical elements 103 to 107 comprise an optical system for acting upon object laser beam L11, and a transmissive LCD display unit 108 is also provided for further acting upon object laser beam L11. Optical elements 109 to 111 comprise an optical system for acting upon reference laser beam L12. Finally, an electromotive stage 113 is provided for holding a hologram recording medium 112 upon which object laser beam L11 and reference laser beam L12 converge, and for moving hologram recording medium 112 as required.
The optical system for acting upon object laser beam L11 includes the following optical elements sequentially disposed along the optical axis of the path of object laser beam L11. A total reflection mirror 103 is first provided for changing the direction of beam L11. Beam L11 then passes through a first cylindrical lens 104 that diffuses beam L11 in a one dimensional direction. A collimator lens 105 receives beam L11 and forms beam L11 into a plurality of parallel laser beams. A projecting lens 106 and a second cylindrical lens 107 are also provided for guiding beam L11 to hologram recording medium 112. Display unit 108 is disposed along the light path of beam L11, and comprises a transmission type liquid crystal panel disposed between the collimator lens 105 and the projecting lens 106. Image data output from an image processing portion (not shown) is displayed on the display unit 108.
The optical system for acting upon reference laser beam L12 includes the following optical elements sequentially disposed along the optical axis of the path of reference laser beam L12. A cylindrical lens 109 is first provided for diffusing beam L12 in a one dimensional direction. Beam L12 the passes to a collimator lens 110 that forms diffused beam L12 into a plurality of parallel laser beams. A total reflection mirror 111 for changing the transmission direction of reference laser beam L12 to arrive at hologram recording medium 112 is also provided.
Hologram recording medium 112 comprises, for example, a photosensitive film. As shown in FIG. 17(B) as well as FIG. 17(A), medium 112 is held by an electromotive stage 113. When electromotive stage 113 is moved, medium 112 is intermittently moved as desired in a direction indicated by an arrow b.
During operation, laser beam L10 is emitted from laser-beam source 101 incident on half mirror 102, as shown in FIG. 17(A). Half mirror 102 splits laser beam L10 into object laser beam L11 and reference laser beam L12. Object laser beam L11 is incident on display unit 108 through first cylindrical lens 104 and collimator lens 105. When object laser beam L11 passes through display unit 108, object laser beam L11 is image-modulated in accordance with an image displayed on display unit 108. Modulated object laser beam L11 is incident on recording medium 112 after passing through projecting lens 106 and second cylindrical lens 107. Reference laser beam L12 is incident on recording medium 112 through the optical system composed of cylindrical lens 109, collimator lens 110 and total reflection mirror 111. Interference fringes generated between the reference beam and the modulated object beam are sequentially recorded in the form of oblong or dot shapes on recording medium 112. These recorded interference fringes form the hologram. Hologram recording medium 3 is structured as shown in FIG. 15, and is used for recording the hologram. Hologram recording medium 3 is a so-called film coating type recording medium incorporating a film base 4 in the form of a tape on which a photopolymer layer 5 composed of photopolymerization-type photopolymers is formed. The photopolymer layer 5 is then coated with a cover sheet 6.
Referring next to FIGS. 16(A)-16(C), the principle of exposing and recording a hologram on hologram recording medium 3 will be described. Photopolymerization-type photopolymers composing the photopolymer layer 5 of hologram recording medium include monomers M initially regularly dispersed among matrix polymers, as shown in FIG. 16 (A). When the photopolymerization-type photopolymers are irradiated with a laser beam LA having power of approximately 10 mJ/cm2 to 400 mJ/cm2, monomers M are polymerized into polymers in the exposed portion, as shown in FIG. 16(B). As the polymerization of the photopolymerization-type photopolymers proceeds, the refractive index between the exposed portions and the non-exposed portions is modulated in accordance with the resulting nonuniformity of the concentration of monomers M caused from movement of monomers M upon exposure. Thereafter, the surface of the photopolymerization-type photopolymers is irradiated with ultraviolet rays or visible light LB having power of about 1000 mJ/cm2 so that polymerization of the monomers M is completed and the position of the monomers are fixed as shown in FIG. 16(c). The refractive index of the photopolymerization-type photopolymers which constitute the photopolymer layer 5 has therefore been changed by the incident laser beam LA. In this manner, interference fringes generated between an object laser beam and a reference laser beam are exposed and recorded on the hologram recording medium 3.
The holographic stereogram producing apparatus 100 depicted in FIGS. 17(A) and 17(B) uses a recording medium such as hologram recording medium 3 of FIG. 15. One of the benefits of such a recording medium is that no special developing process is required after the exposing process has been performed. Thus, the structure of holographic stereogram producing apparatus 100 can be simplified because a developing unit and so forth can be omitted. Moreover, a holographic stereogram can quickly be produced.
Because hologram recording medium 3 incorporates the photopolymer layer 5 constituted by the photopolymerization-type photopolymers, exposure of the recording medium to light has a detrimental effect on the recording medium, and may sensitize the recording medium. Therefore, hologram recording medium 3 must be loaded into the holographic stereogram producing apparatus 100 in the dark. Complicated handling must be performed to insure that light does not reach the recording medium during loading. Moreover, holographic stereogram producing apparatus 100 must also move the recording medium to the exposing and recording portion in the dark.
Vibrations felt by holographic stereogram producing apparatus 100 cause problems during recording. When small vibrations on the order of the wavelength of laser beam L10 are exerted on the recording medium 112, the interference fringes which are to be sequentially exposed and recorded on recording medium 112 become unstable. Thus, a portion of the hologram to be recorded will have its diffraction efficiency and brightness deteriorated. When larger vibrations are felt by holographic stereogram producing apparatus 100, recording of the hologram on recording medium 112 cannot be performed. When portions of the hologram have been exposed and recorded on the recording medium 112 when the diffraction efficiency is unsatisfactorily low because of vibrations, these portions of the hologram will be reproduced as a darker image. Thus, uniformity of the image deteriorates.
Therefore, holographic stereogram producing apparatus 100 is generally provided with a vibration isolator for isolating external vibrations and quickly attenuating vibrations so that recording can be properly performed. The vibration isolator typically comprises an air damper or springs appropriately disposed between a substrate on which laser-beam source 101 and the optical elements constituting the optical hologram recording system are mounted and the housing of the apparatus.
While prevention of external vibrations is important, it is equally important for holographic stereogram producing apparatus 100 to prevent vibrations of recording medium 112 relative to the optical elements which may be generated by the apparatus for holding and moving recording medium 112. Recording medium 112 must be securely held to prevent small vibrations similar in size to the wavelength of laser beam L10 during recording of the hologram on recording medium 112. When a portion of the hologram has been recorded on recording medium 112, the guide means and the moving means recording medium 112 must be quickly moved so that other portions can be recorded. When the movement of recording medium 112 is stopped, vibrations created during movement must be quickly damped. In a conventional holographic stereogram producing apparatus about two seconds have been required for damping vibrations created by the movement of recording medium 112 before recording thereon can be performed. As a result, the production time of one holographic stereogram is increased.
Therefore, another conventional holographic stereogram producing apparatus is provided with a moving mechanism incorporating a guide and a moving apparatus in place of electromotive stage 113 for preventing vibrations of the hologram recording medium 112. The recording medium is disposed on two parallel rollers each having a predetermined tension imparted thereon by a torsion coil spring or the like. The object laser beam and the reference laser beam are incident on the recording medium while an optical element is in direct contact against the recording medium. Only xc2xc of the time is required for damping vibrations created by the movement of the recording medium. However, such a guide and a moving apparatus require complicated structures. Additionally, because the optical element is maintained in contact with the recording medium, the optical element may be worn and damaged. As a result, maintenance of the holographic stereogram producing apparatus is required after it has produced a predetermined number of holographic stereograms. The optical elements are removed, polished, and remounted in the apparatus, or new elements are used. However, because the optical elements must be perfectly aligned, this maintenance cannot be easily performed.
In yet another conventional holographic stereogram producing apparatus another mechanism for moving the recording medium that does not employ a torsion coil spring is used. Rather, a motor constantly inversely rotates a slip member. The force of these rotations are transmitted to one of a plurality of parallel rollers so as to generate a predetermined torque thereon for moving the recording medium. However, the motor in this design is rotated during recording, creating internal vibrations. The quality of the produced holographic stereogram deteriorates because of these vibrations.
Another problem encountered by a conventional holographic stereogram producing apparatus is that dust may enter the apparatus and adhere to the recording medium. This dust can reduce the clarity of the recording of the hologram. Therefore, the conventional holographic stereogram producing apparatus is provided with a cleaning member for cleaning the recording medium. The cleaning member comprises, for example, unwoven fabric which slides on the surface of the recording medium 112 so as to wipe and remove dust and the like adhered to the surface. To allow for proper cleaning, the cleaning member is changed after a predetermined number of holographic stereogram have been produced. The holographic stereogram producing apparatus must be opened to change the cleaning member. When opened, light entering the apparatus may undesirably expose the recording medium.
Furthermore, the conventional holographic stereogram producing apparatus is provided with a mechanism for supplying index matching solution between the hologram recording medium and the optical element to assist in matching the refractive indexes thereof to reduce reflections of light. Since this index matching solution is used up during use of the apparatus when recording holograms, the index matching solution must be replenished by opening the holographic stereogram producing apparatus.
Therefore, it would be beneficial to provide an improved system for recording holograms that overcome the drawbacks of the prior art.
Accordingly, it is an object of the invention to provide a light shielding cartridge for loading into a hologram recording apparatus that accommodates a hologram recording medium.
It is another object of the invention to provide an improved hologram recording apparatus that allows for reduced vibrations, ease of use and ease of maintenance.
A still further object of the invention is to provide an improved hologram recording apparatus that employs a cartridge for holding, advancing and cleaning a recording medium, and that reduces internal vibrations of the hologram recording apparatus.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.
Generally speaking, in accordance with the invention, a cartridge for holding a hologram-image recording medium is arranged to be mounted on a hologram-image recording apparatus. The cartridge allows for sequentially recording interference fringes produced by a modulated object laser beam and a reference laser beam on a hologram recording medium. The cartridge comprises a light shielding case capable of shielding external light, and accommodating a core around which an elongated hologram recording medium is wound. During use, the hologram recording medium is unreeled from the cartridge to be properly positioned at a recording portion of the recording apparatus through an opening provided in the light shielding case.
The cartridge may be further provided with an optical element formed integral therewith for guiding movement of the hologram recording medium. The cartridge for a hologram-image recording medium is provided with a plurality of elements that normally require maintenance, such as a cleaning surface or the like. Rather performing such maintenance, upon using up all of the recording medium, a new cartridge is inserted, and including all new elements that otherwise would require maintenance. Thus, maintenance that risks improperly exposing the recording medium need not be performed.
The cartridge for a hologram-image recording medium may also be provided with a braking apparatus for exerting a load on the hologram recording medium against the direction of movement. This reduces vibrations generated during movement.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts that are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.